Sunday 8 January 2006 06.00 EST
First published on Sunday 8 January 2006 06.00 EST

Mother's Milkby Edward St AubynPicador £12.99, pp279

Before I meet Edward St Aubyn, I swot up on him. Here are a few of the things that I read: that he wears too-tight tweed suits and green velvet smoking jackets; that he is facetious, arrogant and a terrible snob; that his manner is cold and his eyes like those of a 'shark'; that his charm, wit and elegant sentences are reserved for close friends; that these friends include people with grand surnames of which I'm vaguely aware (Rothschilds, Guinnesses, Spencers) but am not smart enough to encounter at 'weekend house parties'. And then, of course, there is the treacherous territory of the life from which he has, at least in part, hewn several novels. As a child, he was raped by his father. At 16, he was a spectacularly focused heroin addict. At 28, he decided that he would kill himself if he did not finish writing a novel. This is as forbidding a potted character analysis as any I have read.

Still, I was desperate to meet him. St Aubyn's new novel, Mother's Milk, is so good - so fantastically well-written, profound and humane - that all the other stuff, even the inhospitable biography, bleaches to grey beside it. He will be glad about this. In spite of his rare talent, St Aubyn has long been the victim of both inverted snobbery and of a certain kind of literary voyeurism whereby critics have often been as keen to find out which bits of his books are true as they have to point out how deft is his style, how mordant and dark his characters.

In the early 1990s, when he published Some Hope, a trilogy (Picador reissue, £12.99) about a character not unlike himself called Patrick Melrose, he initially avoided interviews. Then, one day, he just came out with it. A journalist asked him: 'So you wrote about a five-year-old being raped by his father because that's what happened to you?' After a pause, he replied: 'Yes. Why not say that?' After this, there was no going back. These days, he does not regret his honesty - why should he? - but it is a bore, being dragged down this narrow, briared path all over again.

Mother's Milk takes up Patrick's story once more. He has children now, and a wife too tired for sex. His hated father died in volume two of Some Hope. Patrick, raddled by heroin, goes to New York to collect his ashes - but his mother, a do-gooder whose charity never begins at home, is now busy donating the family house in the south of France to an Irishman with sharp eyes and a spurious New Age foundation to run. Patrick is full of rage about this, and drinking too much, and conducting an affair with an old girlfriend while his wife patiently - too patiently - brings up his sons.

The Patrick Melrose of Mother's Milk is so far from the Patrick of Some Hope that it is sometimes hard to believe they are the same person. The young Patrick, for all that he is screwed up and miserable and in search of redemption, is cruel and sarcastic and somehow apart from the world. This new Patrick, for all that he is in the throes of a powerful mid-life crisis, is kinder, and implicitly shot through with resolve to break the cycle of misery - Larkin's coastal shelf - that passes slowly from one generation to the next. He has also rather noticeably transferred his rage from his father to his mother.

'I wanted this book to be completely independent of the trilogy,' St Aubyn says. 'Some Hope is complete. This is the starting of another story. But at the same time, I didn't want to go through the pseudo-originality of creating another person. The mother is like the mother in Some Hope. She and Patrick have conflicting ideas of goodness.' Is Patrick's rage connected to his mother's ignorance of what his father was doing to him? 'He's not angry at her failure to protect him, but I suppose that is implied when he refers to the continuity between her behaviour then, and her behaviour now.'

Today, St Aubyn is not in tweed; rather, he is an expensive funeral of black cord and grey cashmere. Thanks to his reddish curls and the alabaster sweep of his forehead, he looks boyish for his years, especially for one whose life has been so hard-lived. We meet in a club in Notting Hill, and his voice is so low and languorous, I often struggle to hear it. It is obvious that he dislikes doing interviews, but sarcastic and rude he is not.

I suspect that he is far too clever - not to mention too much of an outsider himself - to be a truly devout snob. He was, however, born in 1960 in a part of Cornwall that has been inhabited by St Aubyns since the Norman conquest and, as a young man, was in possession of a fortune sizeable enough that he did not have to work (this is almost certainly no longer the case). The Daily Mail's profile writers always like to mention that he is a cousin of Lord St Levan, whose home is St Michael's Mount, and that he is godfather to Earl Spencer's son, Louis.

His father did everything and nothing, and dragged his family around the south of France. It was there that the abuse began. 'It splits you in half,' he once said of it. 'You can't accept that your father is doing this shameful thing to you and you take on the shame yourself.' It did not stop until Edward was eight, when he confronted his father. Soon after, his parents divorced (the two events were not connected; his mother did not find out what had happened until her son was grown up) and he was sent to Westminster School. He began taking drugs while he was there, a habit he continued at Oxford (best friend: Will Self). He turned up for his finals immaculately attired, but with heroin secreted about his person and the empty tube of a Bic biro through which to snort it (no pen with which to scribble, though). Four years later, he was a mess. He desperately wanted to write, but his story was painful and elusive. So he began seeing a therapist and, in talking about what was on his mind, won himself a kind of freedom. His father died in 1986.

'Once I started writing, I decided to stop the analysis. I didn't need it any more. But I knew it was good because I went to see my analyst after making a suicide attempt. I was very, very precarious and then I felt a lot better. I stopped feeling mad; there was some sense of order.' Is writing its own kind of therapy? 'If it does have any therapeutic value, the only way to get access to it is to write without any therapeutic intent. You transform experience into, for want of a better word, art. I'm interested in structure and character. Otherwise it would be very boring for everyone else.' But its therapeutic value may also lie simply in the fact that it is work. 'That's what Freud says: work and love. They help convert the extraordinarily depressed into the ordinarily depressed.'

He used to find writing almost intolerably traumatic. He wrote most of Some Hope with a towel round his waist; he was so sweating so much, there was no point putting on a shirt. Is it still so hard? 'Writing Never Mind [the first volume of Some Hope] was an extreme transgression. I'd been told by my father that if I ever told anyone about what had happened, he would kill me. So to write a novel about it was an enormous transgression. Then, when I was writing Bad News [in which Patrick spends most of the book scoring and shooting up], I got very disturbed by writing about my experiences.'

St Aubyn doesn't read his reviews, but he does get 'a team of allies' to tell him if they're any good or not. 'Occasionally, they tell me there's one I could read myself. It's not that I'm aloof or cool about it. On the contrary. But, ultimately, it's about being able to go on writing; I don't want to get stuck with one person's judgment.'

When Some Hope was first published, his style was compared to that of Waugh - a mixed blessing. Though flattering, it was part and parcel of his perceived poshness, and that pushed him into a particular ghetto. People saw his humour, his waspishness, his class-bound, beady English eye, but none of the things that really set him apart: his lovely similes; the careful cadences of his prose; and, most of all, his insight, his (albeit low-key) universality.

Mother's Milk is surely set to change this. Its minute-by-minute interior monologues, its foetid, man-in-a-crisis confusions bring Updike to mind, while its social set-pieces, its brittle, poised dialogue, are as fine as anything in the work of his friend, Alan Hollinghurst. But there is also a new sweetness here, and at times, particularly when he is writing about children, it is heart-stopping.